Hydropower short-term response capability and operating flexibility are critical in some electricity systems, especially during peak demand periods. However, operational variability at hydro plants may originate relevant water flow fluctuations (i.e., hydropeaking) that cause severe alterations in stream ecosystem functionality. Such harmful consequences could be reduced if other energy storage were available.The increasing use of electric vehicles (EVs) has presented the application of their batteries for energy grid scale accumulation purposes. EV interaction with the grid and other renewable energy (RE) sources (primarily wind and solar) has been broadly studied. It seems, however, that EV energy storage allocation to mitigate hydropeaking impacts at regional or national scale remains unexplored. This article evaluates the possibility of using EV batteries to provide the system with additional storage capacity to support a more balanced hydropower operation.The analysis is performed for eight countries with diverse socioeconomic and technological environments. Initially, the coherency in the orders of magnitude between hydropower generation and energy storage capacity is evaluated by calculating the accumulation potential of the current passenger car parc in a hypothetical scenario in which the complete fleet is electrified and suited for vehicle-to-grid (V2G) interaction. After validating the feasibility of the proposal, a long-term analysis is performed using diverse energy, EV rates, and battery capacity forecasts gathered from reliable sources. The results indicate that a 50% PEV fleet using 300 Wh/kg batteries may provide stable storage capacity for average daily hydropower 2050 projections in China, Germany, Japan, Spain and the United States.